Severed traveling-wave tube with external terminations



March 3, 1964 w. H. CHRISTOFFERS ETAL 3,123,736

SEVERED TRAVELING-WAVE TUBE WITH EXTERNAL TERMINATIONS Filed March 22, 1962 3 Sheets-Sheet 1 a /gw/ March 1964 w. H. CHRISTOFFERS ETAL 3,123,736

SEVERED TRAVELING-WAVE TUBE WITH EXTERNAL TERMINATIONS Filed March 22, 1962 3 Sheets-Sheet 2 March 3, 1964- w. H. CHRISTOFFERS ETAL 3,123,736

SEVERED TRAVELING-WAVE TUBE WITH EXTERNAL TERMINATIONS Filed March 22, 1962 3Sheets-Sheet 3 hummer. M0444 464401700240,

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United States Patent i 3,123,736 SEVERE!) TRAVELHNG-WAVE TUBE WITH EXTHEPJJAL TERMIL'NATIQNS William H. Christoiters, Torrance, and John E. Nevins, .lr., Les Angeies, Calif assignors to Hughes Aircraft Company, Culver City, Calif., a corporation of Delaware Filed Mar. 22, 1962, Ser. No. 181,533 12 Claims. (Cl. 315--3.6)

This invention relates generally to traveling-wave tubes, and more particularly relates to a severed traveling-wave tube having termination means external to the slow-wave structure at adjacent ends of the severed amplifying sections.

In traveling-wave tubes a stream of electrons is caused to interact with a propagating electromagnetic wave in a manner which amplifies the electromagnetic energy. In order to achieve such interaction, the electromagnetic wave is propagated along a slow-wave structure, such as a conductive helix wound about the path of the electron stream or a folded waveguide type of structure in which a waveguide is effectively wound back and forth across the path of the electrons. The slow-wave structure provides a path of propagation for the electromagnetic wave which is coniderably longer than the axial length of the structure, and hence, the traveling-wave may be made to effectively propagate at nearly the velocity of the electron stream. The interactions between the electrons in the stream and the traveling-wave cause velocity modulations and bunching of the electrons in the stream. The net result may then be a transfer of energy from the electron beam to the wave traveling along the slow-wave structure, which wave will hereinafter be termed the circuit wave.

The present invention is primarily, although not necessarily, concerned with traveling-wave tubes utilizing slowwave structures of the coupled cavity, or interconnected cell, type. In this type of slow-Wave structure a series of interaction cells, or cavities, are disposed adjacent to each other sequentially along the axis of the tube. The electron stream passes through each interaction cell, and electromagnetic coupling is provided between each cell and the electron stream. Each interaction cell is also coupled to an adjacent cell by means of a coupling hole at the end wall defining the cell. Generally, the coupling holes between adjacent cells are alternately disposed on opposite sides of the axis of the tube, although various other arrangements for staggering the coupling holes are possible and have been employed. When the coupling holes are so arranged, a folded waveguide type of energy propagation results, with the circuit wave energy traversing the length of the tube by entering each interaction cell from one side, crossing the electron stream and then leaving the cell from the other side, thus traveling a sinuous, or serpentine, extended path.

in order to ensure stability, high gain traveling-wave tubes have been constructed in several amplifying sections with a substantially complete sever, or circuit wave isolation, provided between adjacent amplifying sections, and the only coupling between the sections occurring by means of the velocity modulated electron beam. Each amplifying section has a length appropriate for maximum stable gain, and hence it becomes necessary to terminate each section in a matched load.

In the past the necessary terminations have been provided within the slow-wave structure itself, and hence are termed internal terminations. In such arrangements one or more attentuatin'g elements, such as lossy ceramic buttons, are disposed in the slow-wave structure at adjacent ends of the amplifying sections. The lossy material absorbs circuit wave energy reaching the ends of the sections and thus effectively terminates the sections. However, when designing traveling-wave tubes which operate "ice with higher average power ratings, over wider bandwidths, and throughout greater temperature ranges, it becomes necessary to develop terminating devices more suitable for such operation.

Accordingly, it is a principal object of the present invention to provide improved termination means for a severed traveling-wave tube which facilitates stable opera tion of the tube over larger ambient temperature ranges, while maintaining wide bandwidth and high average power rating.

It is a further object of the present invention to provide a terminating device for a severed traveling-wave tube which is relatively insensitive to the particular dielectric properties and geometry of the attenuating material used.

It is a still further object of the present invention to provide a termination for a high power, severed travelingwave tube having an improved impedance match with the slow-wave circuit, especially at the edges of the tube passband, and throughout a wide variation in operating temperatures.

It is a still further object of the present invention to provide a wide bandwidth severed traveling-Wave tube which is capable of handling higher average powers and which is more insensitive to changes in ambient temperature than prior art tubes.

In accordance with the foregoing objectives, the traveling-wave tube of the present invention includes a slowwave structure for supporting energy exchange between a stream of electrons and circuit wave energy propagated along the slow-wave structure. The slow-wave structure is severed into a plurality of amplifying sections and includes means for precluding the passage of circuit wave energy between adjacent amplifying sections while permitting the passage of the electron stream between the sections. Waveguides are disposed externally of the slow wave structure and are coupled to the slow-wave structure in the vicinity of the severed ends of the adjacent amplifying sections. An attenuator is disposed in each waveguide for absorbing circuit wave energy coupled into the waveguide from the associated amplifying sections, thereby terminating the section.

Other and further objects, advantages, and characteristic features of the present invention will become readily apparent from the following detailed description of preferred embodiments or" the invention when taken in conjunction with the appended drawings in which:

FIG. 1 is an over-ail view partly in longitudinal section and partly broken away of a traveling-wave tube constructed in accordance with the present invention;

FlG. 2 is a longitudinal sectional view of a portion of the tube illustrated in FIG. 1 which includes an isolation section;

FIG. 3 is a cross-sectional view taken along line 33 t FIG. 2;

PEG. 4 is a longitudinal sectional view of a portion of v a traveling-wave tube, including an isolation section, constructed according to another embodiment of the present invention; and

FIG. 5 is a cross-sectional View taken along line 5-5 of FIG. 4.

Referring now to the drawings, and more particularly to FIG. 1, the reference numeral it designates generally a traveling-wave tube'which includes an arrangement 12 of magnets, pole pieces and spacer elements which will be described in detail later with respect to FIG. 2. At this point it should sufdce to state that the spacer elements and interior portions of the pole pieces function as a slow-wave structure, while the magnets and pole pieces constitute a periodic focusing device for the electron beam traversing the length of the slow-wave structure.

Coupled to the input end of the arrangement 12 is an input waveguide transducer 14 which includes an impedance step transformer 16. A flange 18 is provided for coupling the assembled traveling-wave tube to an external waveguide or other microwave transmission line (not shown). The construction of the flange 18 may include a microwave window (not shown) transparent to microwave energy but capable of maintaining a vacuum within the traveling-wave tube 10. At the output end of the arrangement 12 an output transducer 20 is provided which is substantially similar to the input transducer 14 and which includes an impedance step transformer 22 and a coupling flange 24, which elements are similar to the elements 16 and 18, respectively, of the input transducer 14. For vacuum pumping or out-gassing the travelingwave tube 10 during manufacture, a double-ended pumping tube 26 is connected to both of the input and output waveguide transducers 14 and 20.

An electron gun 28 is disposed at one end of the traveling-wave tube 10 which, although illustrated as the input end in FIG. 1, may alternatively be the output end if a backward wave device is desired. The electron gun 28 functions to project a stream of electrons along the axis of the tube 10 and may be of any conventional construction well known in the art. For details as to the construction of the gun 28 reference is made to Patent No. 2,985,791, entitled Periodically Focused Severed Traveling-Wave Tube, issued May 23, 1961 to D. J. Bates et al. and assigned to the assignee of the present invention and to Patent No. 2,936,393, entitled Low Noise Traveling-Wave Tube, issued May 10, 1960 to M. R. Currie et al. and assigned to the assignee of the present invention.

At the output end of the traveling-wave tube 10 there is provided a cooled collector structure 30 for collecting the electrons in the stream. The collector is conventional and may be of any form well known in the art. For details as to the construction of the collector, reference is made to the aforesaid Patent No. 2,985,791 and to Patent No. 2,860,277, entitled Traveling-Wave Tube Collector Electrode issued November 11, 1958 to A. H. Iversen and assigned to the assignee of the present invention.

The construction of the slow-wave structure, focusing system, and terminations of the traveling-wave tube 10 are illustrated in more detail in FIG. 2. A plurality of essentially annular disk-shaped focusing magnets 32 are interposed between a plurality of ferromagnetic pole pieces 34. As is illustrated in FIG. 3, the magnets 32 may be diametrically split into two sections 32a and 32b for convenience during assembly of the tube. The ferromagnetic pole pieces 34 extend radially inwardly of the magnets 32 to approximately the perimeter of the region adapted to contain the axial electron stream. The individual pole pieces are constructed in such a manner that a short drift tube, or ferrule, 36 is provided at the inner extremity of each pole piece. The drift tube 36 is in the form of a cylindrical extension, or lip, protruding axially along the path of the electron stream from both surfaces of pole piece 34, i.e., in both directions normal to the plane of the pole piece 34. The drift tubes 36 are provided with central and axially aligned apertures 38 to provide a passage for the flow of the electron beam. Adjacent ones of the drift tubes 36 are separated by a gap 40 which functions as a magnetic gap to provide a focusing lens for the electron beam and also as an interaction gap in which energy exchange between the electron beam and circuit wave energy traversing the slow-wave structure occurs.

Disposed radailly within each of the magnets 32 is an annular slow-wave circuit spacer element 42 of a conductive non-magnetic material such as copper. Each spacer element has a central cylindrical aperture 44 to provide space for a microwave interaction cell, or cavity, 46 which is defined by the inner lateral surface of the spacer 42 and the walls of the two adj P Places 34 projecting inwardly of the spacer element 42. The inner diameter of the spacer 42 determines the radial extent of the interaction cell 46, while the axial length of the spacer 42 determines the axial length of the cell 46.

For interconnecting adjacent interaction cavities 46 an off-center coupling hole 4-8 is provided through each of the pole pieces 34 to permit the transfer of circuit wave energy from cell to cell. As is illustrated in FIGS. 2 and 3, the coupling holes 48 may be substantially kidneyshapcd and may be alternately disposed apart with respect to the drift tubes 36. It should be pointed out, however, that the coupling holes 48 may be of other shapes and may be staggered in various other arrangements, such as those disclosed in Patent No. 3,010,047, entitled Traveling-Wave Tube, issued November 21, 1961 to D. J. Bates and assigned to the assignee of the present invention. In any event, it will be apparent that the spacer elements 4-2 and the portions of the pole pieces 34 projecting inwardly of the spacers 42 not only form an envelope for the tube, but also constitute a slow-wave structure for propagating circuit wave energy in a serpentine path along the axially traveling electron stream so as to support energy exchange between the electrons of the stream and the circuit wave.

The axial length of the magnets 32, hence that of the spacers 42, is equal to the spacing between adjacent pole pieces 34, and the radial extent of the magnets 32 is approximately equal to or, as shown, slightly greater than that of the pole pieces 34. To provide focusing lenses in the gaps 40, the magnets 32 are stacked with alternating polarity along the axis of the tube, thus causing a reversal of the magnetic field at each magnetic lens and thereby providing a periodic focusing device. It should be pointed out, however, that although the lengths of the spacers 42 may be substantially constant, they may also be varied slightly with respect to each other so that the effective axial length of the cavities 46 is varied as a function of distance along the tube to ensure that the desired interaction between the electron stream and the traveling waves will continue to a maximum degree even though the electrons are decelerated toward the collector end of the tube. For such arrangements reference is made to Patent No. 2,956,200, entitled Periodically Focused Traveling-Wave Tube With Tapered Phase Velocity, issued October 11, 1960 to D. J. Bates and assigned to the assignee of the present invention.

As has been pointed out above, in order to ensure stability and freedom from oscillations on account of possible regenerative feedback, high gain traveling-wave tubes of the type with which the present invention is concerned may be constructed in several amplifying sections. Thus, in FIG. 1, the traveling-wave tube 10 is illustrated as having three amplifying sections 52, 54 and 56, although it is to be understood that three such sections are shown sole ly for illustrative purposes. Each of the amplifying sections is isolated from adjacent sections by means of an isolator section. Thus, in the traveling-wave tube of FIG. 1, the first and second amplifying sections 52 and 54, respectively, are isolated from each other by isolator section 58; while the second and third amplifying sections 54 and 56, respectively, are isolated from one another by means of isolator section 60. The isolator sections 58 and 60 provide a substantially complete sever, or isolation for circuit wave energy, between adjacent amplifying sections of the traveling-wave tube 10, while at the same time allowing the electron stream to pass through the entire length of the traveling-wave tube. The electron stream is modulated in each amplifying section, and hence as it enters the subsequent amplifying section it launches a new circuit wave therein which is amplified by interaction between the new circuit wave and the electron stream. Thus, unidirectional coupling between adjacent amplifying sections is provided through the electron stream.

The isolator section 58 is illustrated in more detail in FIGS. 2 and 3, it being understood that isolator section 60 is constructed in an identical manner. Isolator section 58 is formed in a substantial continuity of the pole piecemagnet-spacer assembly 12. However, a pair of special, or modified, slow-wave circuit spacer elements 42 and 42" are employed in the isolator section instead of the spacer elements 42 ordinarily used in the remainder of the tube, As is illustrated in FIG. 3, the special spacer 42 (spacer 42" being identical to spacer 42') differs from regular spacer 42 in that the special spacer is not completely annular, but possesses an extended circumferential portion on one side which terminates in a flat surface 66 of rectangular cross-section. An elliptical coupling hole 70 is provided in the special spacer 42' from the surface 66 to the central aperture, i.e., to interaction cavity 4'6. A similar coupling hole 72 is provided in special spacer 42".

The pole piece 34 disposed between the two spacers 42 and 42" in the isolation section 58 is identical to the remaining pole pieces except in one significant respect, namely, no coupling hole for circuit wave energy is provided in the pole piece 34'. Therefore, circuit wave energy in amplifying section 52 is precluded from passing into the section 54, and vice versa, thereby achieving circuit wave isolation between the sections 52 and 54-.

In order to dissipate the circuit wave energy entering the isolator section 5% with essentially no reflection back into the amplifying section from whence it came, termination means are disposed externally of the slow-wave structure at the adjacent ends of the amplifying sections 52 and 54. More specifically, a waveguide 62 is disposed between the two pole pieces adjacent to special spacer 42 in that region where a portion of the magnet 32. would have existed in the absence of a termination. The inner end of the waveguide 62 abuts against the surface 66 of the special spacer 42' and is fastened thereto by welding or brazing. Similarly, a Waveguide 64 is disposed between the pole pieces adjacent to the special spacer 42", with the inner of the Waveguide 64 being fastened to the flat surface 68 of the special spacer 42". The magnet sections 32a and 32b which are disposed between the pole pieces in the isolator section 58 have recessed portions to conform to the shape of special spacers 42 and 42" and waveguides 62 and 64. It is, of course, desirable to keep the width of the waveguides 62 and 64 small so as to maintain as much magnetic material as possible between the adjacent pole pieces, although the waveguide width must be large enough to achieve a satisfactory match with the interaction cavities 46' and 46".

Elements 74 and '80 of attenuating material are disposed within the waveguides 62 and 64, respectively, to dissipate circuit wave energy entering the waveguides. The attenuators 74 and 80 may be of lossy ceramic material, for example a mixture of forsterite and silicon carbide, with the percentage of silicon carbide varying from essentially 50% to essentially 80%. Examples of other materials which could be used are silicon carbide and alumina, silicon carbide and talc, silicon carbide and beryllia, or other lossy material and ceramic combinations. As is well known, such materials have reciprocal attenuating properties, i.e. they provide substantially the same attenuation regardless of the direction in which the wave energy traverses the attenuator. As is shown in FIGS. 2 and 3, the attenuator 74 is in a form of a twostep lossy element, i.e., with steps, or surfaces, 76 and 78 disposed in planes perpendicular to the length of the waveguide 62 at different points along the length of the waveguide (attenuator 80 being identical to attenuator 74). The particular dimensions of the attenuators 74 and iii) are determined by the dielectric constant e' and the loss constant e" of the lossy material used and the particular frequencies of the circuit wave energy to be attenuated. The minimum length of the attenuators is selected according to the condition that the circuit wave energy be substantially absorded when it reaches the end of the attenuator remote from the region of coupling to the slow-wave circuit.

A two-step attenuating element simply represents one manner of achieving the necessary dissipation of circuit Wave energy, and alternate forms of attenuators may be employed without departing from the principles of the invention. For example, the attenuating element may have the shape of a rectangular parallelepiped, a stepped element with more than two steps, a pyramid, or a single or multiple wedged-shaped element, with the apex of the wedge or wedges residing at the input end of the waveguide and the thickness of the wedge or wedges reaching full waveguide height at or slightly before the end of the waveguide remote from the region of coupling to the slow-wave circuit. Regardless of the particular geometry of the attenuating element, it should be noted that the attenuating material is disposed in a waveguide which is physically located external to the slow-wave circuit and which is not a part of the slow-wave circuit, with the same type of coupling being employed to couple energy from the slow-wave circuit to the waveguides 62 and 64 as that used to couple energy into the slow-wave circuit from the input waveguide 16 or to couple amplified output energy from the slow-wave circuit to the output waveguide 22.

In the operation of the travelingwave tube it circuit wave energy of microwave frequencies traverses the slowwave structure from the electron gun end to the collector end, being amplified first in section 52 due to its interaction with the electron stream. Near the output of this amplifying section, the circuit wave has grown and has caused considerable charge density modulation in the electron stream. The circuit wave in the section 52 traveling toward the section 54 enters the cavity 46' in the isolator section 58 through coupling hole 48'. However, since there is no circuit wave coupling hole in the pole piece 34, this wave is precluded from entering the next amplifying section 54 and is directed through the coupling hole 79 in the spacer element 42' into the waveguide 62 where it is substantially dissipated in the attenuating element 74. Nevertheless, the modulated electron stream passes through isolator section and into amplifying section d4, launching a new circuit wave in section The new circuit wave is amplified by interaction with the electron stream until reaching isolator section es. Moreover, circuit wave energy in section 54 which is traveling toward the section 52 will enter the isolator section 53 through the coupling hole 38 and pass from the cavity 46" into the waveguide 64 via the coupling hole 72, being substantially absorbed in the lossy attenuating element 52%. The isolator section 69 functions in the same manner as the ection 8 to dissipate circuit wave energy from the section 54 which has traveled toward the collector, as well as circuit wave energy from the section 56 which traveled toward the electron Again, the modulated electron beam passes through the isolator section 6i? and launches a new circuit wave in section 55. This new wave is amplified by interaction with the electron stream in the section 56, and the amplified output wave is fed from the section 53 to the output waveguide transducer 22.

The termination heretofore described is especially suitable for use in a traveling-Wave tube having a permanent magnet periodic focusing system. liowever, the principles of the present invention are in no way limited to perio ically focused tubes but may also be employed in tubes using other types of focusing schemes, such as solenoid focusing or non-periodic permanent magnet focusing. One manner in which the external terminations of the present invention may be used in a solenoid-focused traveling-wave tube is illustrated in FIGS. 4- and 5.

The slow-wave structure of the embodiment of FIGS. 4 and 5 comprises a series of alternating spacer elements 142 and transverse vanes 1134. The elements 142 and vanes 134 are similar to the spacers 42 and the inner portions of the pole pieces 34, respectively, of the embodiment of FIG. 2 exceptthat both the spacers 142 and the vanes 134 may be of a non-magnetic material such as copper. The inner surface 144 of each slow-wave circuit spacer 142 is cylindrical, while the outer surface of each spacer 142 includes a pair of oppositely disposed fiat portions 135 and 137 of rectangular crosssection. Each traverse vane 134, the outer surfaces of which are shaped the same as those of the spacers 142, defines a drift tube, or ferrule, 136 in its central region, which drift tubes are identical with the drift tubes 36 of FIG. 2. The vanes 134 and spacer elements 142 define a series of interaction cavities 146 which are intercoupled through coupling holes 148 in the vanes 134. An interaction gap 140 is provided between each pair of adjacent drift tubes 136.

The electron stream traversing the drift tubes 136 via apertures 138 is focused by means of a solenoid 132 which is concentrically disposed about and longitudinally coextensive with the arrangement of spacers 142 and vanes 134. The inner surface of the solenoid 132 lies adjacent the cylindrical portions of the outer surfaces of the spacer elements 142 and the vanes 134, while the spaces between the solenoid 132 and the fiat portions of the outer surfaces of the spacer elements 142 and the vanes 134 are used to accommodate waveguides 116 and 162164, respectively. The waveguide 116 supports the propagation of electromagnetic wave energy into or out of the slow-wave structure. The waveguides 162 and 164 are termination waveguides and are disposed between the solenoid and the slow-wave structure, with their lengths parallel to the longitudinal axis of the tube, in the vicinity of the region of isolation, or sever, between adjacent amplifying sections 152 and 154 of the tube. The Waveguide 162 is coupled to interaction cavity 146 by means of coupling holes 171 and 170 in the waveguide 162 and spacer element 142, respectively. Similarly, the waveguide 164 is coupled to interaction cavity 146" via coupling apertures 173 and 172. The common wall between the waveguides 162 and 164 may be constructed with portions 163 and 165 projecting obliquely into the respective waveguides 162 and 164 to better direct entering energy around the bend in the waveguide.

A lossy attenuating element 174, which may be of the materials set forth above for attenuators 74 and 80 of FIG. 2, is disposed in the waveguide 162; and a similar attenuator 180 is located in the waveguide 164. As is shown in FlGS. 4 and 5, the attenuators 174 and 180 are in the form of stepped devices, with the respective first steps 176 and 186 thereof located slightly beyond the coupling holes 171 and 173, respectively, and the respective second steps 178 and 188 thereof located further along the waveguides 162 and 154, respectively. Alternately, the attenuators 174- and 139 may be of the various other shapes described above with reference to the attenuating elements 74 and 89 of FIG. 2.

The operation of the terminating means of FIGS. 4 and is similar to that of the terminations of FIGS. 2 and 3. Circuit wave energy traversing amplifying section 152 of the slow-wave structure in the direction of section 154- passes through interaction cavity 146 and coupling holes 170 and 171 into waveguide 162 where it is absorbed by attenuator 174. Circuit wave energy in section 154 traveling toward section 152 passes through interaction cavity 146" and is coupled into waveguide 164 via apertures 172 and 173, this energy being dissipated in the attenuator element 180. The transverse vane 134, of course, prevents circuit wave energy from passing between amplifying sections 152 and 154, although the electron stream is allowed to pass through the vane 134 via the aperture in the drift tube thereof.

The attenuating devices shown and described above are able to attenuate substantially all of the large amounts of circuit wave energy present at the ends of the various amplifying sections in a high power severed travelingwave tube by directing the circuit wave energy to be attenuated into waveguides disposed externally of the slowwave propagating structure and by providing in the wave guides the proper amount of attenuation to dissipate substantially all of the entering circuit wave energy With a minimum amount of energy being reflected back into the slow wave propagating structure. The external termination arrangement achieves proper attenuation of the circuit wave energy throughout an increased range of temperatures while maintaining wide bandwidth operation. Moreover, since the attenuators are located externally of the slow-Wave structure a larger portion of their surface area is available for contact with a suitable coolant (especially in the embodiment of FIG. 4) than with internal terminations, thereby enabling the tube to handle considerably greater amounts of power.

Although the present invention has been shown and described with reference to specific embodiments, numerous modifications or alterations which are obvious to those skilled in the art may be made therein without departing from the spirit and scope of the invention as set forth in the appended claims.

What is claimed is:

l. A traveling-wave tube of the type which is severed into a plurality of amplifying sections comprising in combination:

(a) means for launching an electron stream along a predetermined path of fixed length;

(12) slow-wave structure means in each of said amplifying sections and disposed along said path for propagating circuit Wave energy and providing energy exchange between said stream of electrons and said circuit wave energy;

(c) means disposed between at least one pair of adjacent amplifying sections for precluding the passage of circuit wave energy between said adjacent amplitying sections While permitting the passage of said electron stream therebetween and (:1) means disposed externally of said slow-wave structure means adjacent at least one end of at least one of said adjacent amplifying sections for absorbing circuit wave energy.

2. A traveling-wave tube comprising in combination:

(a) an envelope;

(b) means disposed adjacent one end of said envelope for launching an electron stream along a predetermined path within said envelope;

(0) means disposed within said envelope and cooperating therewith to form a wave propagating structure for supporting energy exchange between electrons of said electron stream and circuit Wave energy propagated along said wave propagating structure;

(d) said wave propagating structure being divided into a plurality of amplifying sections isolated from one another with respect to circuit wave energy; and

(2) means disposed externally of said envelope adjacent at least one end of each pair of adjacent amplifying sections for absorbing circuit wave energy.

3. A traveling-wave tube of the type which is severed into a plurality of amplifying sections, each isolated from one another with respect to circuit wave energy comprising in combination:

(a) means for launching a stream of electrons along a predetermined path of fixed length;

(12) a wave propagating structure disposed along and about said path for propagating circuit wave energy in such manner that it interacts with said stream of electrons;

(0) means disposed between each pair of adjacent amplifying sections for precluding the passage of circuit wave energy between said adjacent amplifying sections while permitting the passage of said stream of electrons therebetween;

(d) waveguiding means disposed externally of said Wave propagating structure and coupled to said Wave propagating structure adjacent said precluding means; and

(e) loss means disposed in said waveguiding means for attenuating circuit wave energy.

60 is constructed in an identical manner. Isolator section 58 is formed in a substantial continuity of the pole piecemagnet-spacer assembly 12. However, a pair of special, or modified, slow-Wave circuit spacer elements 42' and 42" are employed in the isolator section instead of the spacer elements 42 ordinarily used in the remainder of the tube. As is illustrated in FIG. 3, the special spacer 42 (spacer 42 being identical to spacer 42') differs from regular spacer 42 in that the special spacer is not completely annular, but possesses an extended circumferential portion on one side which terminates in a fiat surface 66 of rectangular cross-section. An elliptical coupling hole 7 th is provided in the special spacer 42 from the surface 66 to the central aperture, i.e., to interaction cavity 46. A similar coupling hole 72 is provided in special spacer 42".

The pole piece 34' disposed between the two spacers 42 and 42" in the isolation section 58 is identical to the remaining pole pieces except in one significant respect, namely, no coupling hole for circuit wave energy is provided in the pole piece 34'. Therefore, circuit wave energy in amplifying section 52 is precluded from passing into the section 54, and vice versa, thereby achieving circuit wave isolation between the sections 52 and 54.

In order to dissipate the circuit wave energy entering the isolator section 58 with essentially no reflection back into the amplifying section from whence it came, termination means are disposed externally of the slow-wave structure at the adjacent ends of the amplifying sections 52 and 54. More specifically, a waveguide 62 is disposed between the two pole pieces adjacent to special spacer 42' in that region where a portion of the magnet 32 would have existed in the absence of a termination. The inner end of the waveguide 62 abuts against the surface 66 of the special spacer 4-2 and is fastened thereto by welding or brazing. Similarly, a Waveguide 64 is disposed between the pole pieces adjacent to the special spacer 42", with the inner of the waveguide 64 being fastened to the fiat surface 68 of the special spacer 42". The magnet sections 32a and 321) which are disposed between the pole pieces in the isolator section 58 have recessed portions to conform to the shape of special spacers 4-2 and 42" and waveguides 62 and 64. It is, of course, desirable to keep the Width of the waveguides 62 and 64 small so as to maintain as much magnetic material as possible between the adjacent pole pieces, although the waveguide width must be large enough to achieve a satisfactory match with the interaction cavities 46' and 46".

Elements '74 and 8d of attenuating material are disposed within the waveguides 62 and 64, respectively, to dissipate circuit Wave energy entering the waveguides. The attenuators 74 and 89 may be of lossy ceramic material, for example a m xture of forsterite and silicon carbide, With the percentage of silicon carbide varying rom essentially 50% to essentially 80%. Examples of other materials which could be used are silicon carbide and alumina, silicon carbide and talc, silicon carbide and beryllia, or other lossy material and ceramic combinations. As is well known, such materials have reciprocal attenuating properties, i.e. they provide substantially the same attenuation regardless of the direction in which the wave energy traverses the attenuator. As is shown in FIGS. 2 and 3, the attenuator 74 is in a form of a twostep lossy element, i.e., with steps, or surfaces, 76 and '78 disposed in planes perpendicular to the length of the waveguide 62 at different points along the length of the waveguide (attenuator 80 being identical to attenuator '74). The particular dimensions of the attenuators 74 and 80 are determined by the dielectric constant e and the loss constant e" of the lossy material used and the particulm frequencies of the circuit Wave energy to be attenuated. The minimum length of the attenuators is selected according to the condition that the circuit Wave energy be substantially absorded when it reaches the end of the attenuator remote from the region of coupling to the slow-wave circuit.

A two-step attenuating element simply represents one manner of achieving the necessary dissipation of circuit wave energy, and alternate forms of attenuators may be employed without departing from the principles of the invention. For example, the attenuating element may have the shape of a rectangular parallelepiped, a stepped element with more than two steps, a pyramid, or a single or multiple wedged-shaped element, with the apex of the wedge or wedges residing at the input end of the waveguide and the thickness of the wedge or Wedges reaching full waveguide height at or slightly before the end of the waveguide remote from the region of coupling to the slow-wave circuit. Regardless of the particular geometry of the attenuating element, it should be noted that the attenuating material is disposed in a waveguide which is physically located external to the slow-wave circuit and which is not a part of the slow-wave circuit, with the same type of coupling being employed to couple energy from the slow-wave circuit to the waveguides 62 and 64 as that used to couple energy into the slow-wave circuit from the input Waveguide 16 or to couple amplified output energy from the slow-wave circuit to the output waveguide 22.

In the operation of the traveling-wave tube ltl, circuit wave energy of microwave frequencies traverses the slowwave structure from the electron gun end to the collector end, being amplified first in section 52 due to its interaction with the electron stream. Near the output of this amplifying section, the circuit wave has grown and has caused considerable charge density modulation in the electron stream. The circuit wave in the section 52 traveling toward the section 5% enters the cavity 46 in the isolator section 5% through coupling hole 48'. However, since there is no circuit wave coupling hole in the pole piece 34', this Wave is precluded from entering the next amplifying section 54- and is directed through the coupling hole 71 in the spacer element 42 into the waveguide 62 where it is substantially dissipated in die attenuating element '74. Nevertheless, the modulated electron stream passes through isolator section 58 and into amplifying section 54, launching a new circuit wave in section 54. The new circuit Wave is amplified by interaction with the electron stream until reaching isolator section 6-3. Moreover, circuit wave energy in section 54 which is traveling toward the section 52 will enter the isolator section 58 through the coupling hole 453" and pass from the cavity 46 into the waveguide 64 via the coupling hole 72, being substantially absorbed in the lossy attenuating element 36. The isolator section functions in the same manner as the section 53 to dissipate circuit wave energy from the section 5 which has traveled toward the collector, as Well as circuit wave energy from the section 525 which has traveled toward the electron gun. Again, the modulated electron beam passes through the isolator section 6% and launches a new circuit wave in section This new Wave is amplified by interaction with the electron stream in the section 56, and the amplified output wave is fed from the section 53 to the output waveguide transducer 22.

The termination heretofore described is especially suitable for use in a traveling-wave having a permanent magnet periodic focusing system. However, the principles of the present invention are in no way limited to period- 'cally focused tubes but may also be employed in tubes using other types of focusing schemes, such as solenoid focusing or non-periodic permanent magnet focusing. One manner in which the external terminations of the present invention may be used in a solenoid-focused travelin -wave tube is illustrated in FIGS. 4 and 5.

The slow-wave structure of the embodiment of FiGS. 4 and 5 comprises a series of alternating spacer elements 142 and transverse vanes 134. The elements 142 and vanes 134 are similar to the spacers i2 and the inner por tions of the pole pieces 34, respectively, of the embodiment of FIG. 2 except that both the spacers 142 and the vanes 134 may be of a non-magnetic material such as copper. The inner surface 144 of each slow-wave circuit spacer 142 is cylindrical, while the outer surface of each spacer 142 includes a pair of oppositely disposed fiat portions 135 and 137 of rectangular cross-section. Each traverse vane 134, the outer surfaces of which are shaped the same as those of the spacers 142, defines a drift tube, or ferrule, 136 in its central region, which drift tubes are identical with the drift tubes 36 of FIG. 2. The vanes 134 and spacer elements 142 define a series of interaction cavities 146 which are intercoupled through coupling holes 148 in the vanes 134. An interaction gap 140 is provided between each pair of adjacent drift tubes 136.

The electron stream traversing the drift tubes 136 via apertures 138 is focused by means of a solenoid 132 which is concentrically disposed about and longitudinally coextensive with the arrangement of spacers 142 and vanes 134. The inner surface of the solenoid 132 lies adjacent the cylindrical portions of the outer surfaces of the spacer elements 142 and the vanes 134, while the spaces between the solenoid 132 and the fiat portions of the outer surfaces of the spacer elements 142 and the vanes 134 are used to accommodate waveguides 116 and 162164, respectively. The waveguide 116 supports the propagation of electromagnetic wave energy into or out of the slow-wave structure. The waveguides 162 and 164 are termination waveguides and are disposed between the solenoid and the slow-wave structure, with their lengths parallel to the longitudinal axis of the tube, in the vicinity of the region of isolation, or sever, between adjacent amplifying sections 152 and 154 of the tube. The waveguide 162 is coupled to interaction cavity 146 by means of coupling holes 171 and 170 in the waveguide 162 and spacer element 142, respectively. Similarly, the waveguide 164 is coupled to interaction cavity 146" via coupling apertures 173 and 172. The common wall between the waveguides 162 and 164 may be constructed with portions 163 and 165 projecting obliquely into the respective waveguides 162 and 164 to better direct entering energy around the bend in the waveguide.

A lossy attenuating element 174, which may be of the materials set forth above for attenuators 74 and 80 of FIG. 2, is disposed in the waveguide 162; and a similar attenuator 186 is located in the waveguide 164. As is shown in FIGS. 4 and 5, the attenuators 174 and 180 are in the form of stepped devices, with the respective first steps 176 and 186 thereof located slightly beyond the coupling holes 171 and 173, respectively, and the respective second steps 178 and 188 thereof located further along the waveguides 162 and 164, respectively. Alternately, the attenuators 174 and 180 may be of the various other shapes described above with reference to the attenuating elements 74 and 86 of FIG. 2.

The operation of the terminating means of FIGS. 4 and is similar to that of the terminations of FIGS. 2 and 3. Circuit wave energy traversing amplifying section 152 of the slow-wave structure in the direction of section 154 passes through interaction cavity 146' and coupling holes 170 and 171 into waveguide 162 where it is absorbed by attenuator 174. Circuit wave energy in section 154 traveling toward section 152 passes through interaction cavity 146" and is coupled into waveguide 164 via apertures 172 and 173, this energy being dissipated in the attenuator element 130. The transverse vane 134', of course, prevents circuit wave energy from passing between amplifying sections 152 and 154, although the electron stream is allowed to pass through the vane 134 via the aperture in the drift tube thereof.

The attenuating devices shown and described above are able to attenuate substantially all of the large amounts of circuit wave energy present at the ends of the various amplifying sections in a high power severed travelingwave tube by directing the circuit wave energy to be attenuated into waveguides disposed externally of the slowwave propagating structure and by providing in the waveguides the proper amount of attenuation to dissipate substantially all of the entering circuit wave energy, with a minimum amount of energy being reflected back into the slow wave propagating structure. The external termination arrangement achieves proper attenuation of the circuit wave energy throughout an increased range of temperatures while maintaining wide bandwidth operation. Moreover, since the attenuators are located externally of the slow-wave structure a larger portion of their surface area is available for contact with a suitable coolant (especially in the embodiment of FIG. 4) than with internal terminations, thereby enabling the tube to handle considerably greater amounts of power.

Although the present invention has been shown and described with reference to specific embodiments, numerous modifications or alterations which are obvious to those skilled in the art may be made therein without departing from the spirit and scope of the invention as set forth in the appended claims.

What is claimed is:

l. A traveling-wave tube of the type which is severed into a plurality of amplifying sections comprising in combination:

(a) means for launching an electron stream along a predetermined path of fixed length;

(b) slow-wave structure means in each of said amplifying sections and disposed along said path for propagating circuit wave energy and providing energy exchange between said stream of electrons and said circuit wave energy;

(c) means disposed between at least one pair of adjacent amplifying sections for precluding the passage of circuit wave energy between said adjacent amplifying sections while permitting the passage of said electron stream therebetween and (d) means disposed externally of said slow-Wave structure means adjacent at least one end of at least one of said adjacent amplifying sections for absorbing circuit Wave energy.

2. A traveling-wave tube comprising in combination:

(a) an envelope;

(b) means disposed adjacent one end of said envelope for launching an electron stream along a predetermined path within said envelope;

(0) means disposed within said envelope and cooperating therewith to form a wave propagating structure for supporting energy exchange between electrons of said electron stream and circuit wave energy propagated along said wave propagating structure;

(d) said wave propagating structure being divided into a plurality of amplifying sections isolated from one another with respect to circuit wave energy; and

(2) means disposed externally of said envelope adjacent at least one end of each pair of adjacent amplifying sections for absorbing circuit wave energy.

3. A traveling-wave tube of the type which is severed into a plurality of amplifying sections, each isolated from one another with respect to circuit wave energy comprising in combination:

(a) means for launching a stream of electrons along a predetermined path of fixed length;

(b) a wave propagating structure disposed along and about said path for propagating circuit wave energy in such manner that it interacts with said stream of electrons;

(0) means disposed between each pair of adjacent amplifying sections for precluding the passage of circuit wave energy between said adjacent amplifying sections while permitting the passage of said stream of electrons therebetween;

(d) waveguiding means disposed externally of said wave propagating structure and coupled to said wave propagating structure adjacent said precluding means; and

(a) loss means disposed in said waveguiding means for attenuating circuit wave energy.

4. A traveling-wave tube comprising in combination:

(a) means for launching a stream of electrons along a predetermined path of fixed length;

(b) a wave propagating structure divided into at least first and second amplifying sections and disposed along and about said path for propagating circuit wave energy in such manner that it interacts with said stream of electrons;

(c) means for precluding the passage of circuit wave energy between said first and second amplifying sections while permitting the passage of said stream of electrons therebetween;

(d) first waveguiding means disposed externally of and coupled to said first amplifying section of said wave propagating structure adjacent said precluding means;

(6) second waveguiding means disposed externally of and-coupled to said second amplifying section of said wave propagating structure adjacent said precluding means; and

(1) loss means disposed in each of said first and second waveguiding means for attenuating circuit wave energy.

5. A traveling-wave tube comprising in combination:

(a) means for launching a stream of electrons along a predetermined path of fixed length;

(12) means forming a plurality of groups of intercoupled cavities disposed sequentially along and about said path for propagating circuit wave energy and providing energy exchange between said electron stream and said circuit wave energy;

() means disposed between adjacent end cavities in adjacent ones of said groups for precluding the passage of circuit wave energy between said adjacent end cavities while permitting the passage of said stream of electrons therebetween;

(d) waveguiding means disposed externally of and coupled to each of said end cavities; and

(e) loss means disposed in each said waveguiding means for attenuating circuit wave energy.

6. A traveling-wave tube of the type which is severed into a plurality of amplifying sections, each isolated from one another with respect to circuit wave energy comprising in combination:

(a) means for launching a stream of electrons along a predetermined path of fixed length;

(19) a wave propagating structure for each of said amplifying sections and disposed along and about said path for propagating circuit wave energy in such manner that it interacts with said stream of electrons;

(0) means disposed between each pair of adjacent amplifying sections for precluding the passage of circuit wave energy between said adjacent amplifying sections while permitting the passage of said stream of electrons therebetween;

(d) a first waveguide disposed externally of and coupled to said wave propagating structure of one of said pair of adjacent amplifying sections;

(2) a second waveguide disposed externally of and coupled to said wave propagating structure of the other of said pair of adjacent amplifying sections; and

(1) an element of lossy ceramic material disposed in each of said first and second waveguides, each of said elements having a smaller cross-sectional area at its end nearer the region of coupling to said wave propagating structure than at its end more remote therefrom.

7. A traveling-wave tube comprising in combination:

(a) collector means;

(b) electron gun means for emitting a stream of electrons;

(c) a plurality of axially aligned essentially annular magnets of alternating polarity and a plurality of ferromagnetic pole pieces interposed between and abutting adjacent ones of said magnets for produc ing a periodic magnetic focusing field for constraining said stream of electrons to flow along a predetermined path toward said collector means;

(d) a slow-wave structure divided into a plurality of amplifying sections and disposed between said electron gun means and said collector means for propagating circuit wave energy in such manner that it interacts with said stream of electrons;

(e) said slow wave structure being disposed within and axially aligned with said annular magnets and including means for precluding the passage of circuit wave energy between each pair of adjacent amplifying sections;

(f) first and second waveguides, each disposed externally of and coupled to one of said adjacent amplitying sections of said slow-wave structure in the vicinity of said precluding means;

(g) the lengths of said waveguides being perpendicu- '(a) collector means;

([1) electron gun means for emitting a stream of electrons;

(c) a plurality of axially aligned essentially annular magnets of alternating polarity and a plurality of ferromagnetic pole pieces interposed between and abutting adjacent ones of said magnets for producing a periodic magnetic focusing field for constraining said stream of electrons to fiow along a predetermined path toward said collector means; I

(d) an essentially annular non-magnetic spacer element having an outer diameter essentially equal to the inner diameter of said magnets disposed within each of said magnets;

(e) said pole pieces projecting internally of said spacer elements to define therewith a plurality of groups of intercoupled interaction cavities arranged sequentially along and in electromagnetic interacting relationship with said stream of electrons;

(1) means disposed between adjacent end cavities in adjacent ones of said groups for precluding the passage of circuit wave energy between said adjacent end cavities while permitting the pass-age of said stream of electrons therebetween;

(g) the respective spacer elements defining said end cavities each having a coupling hole through its lateral surface;

(It) a plurality of waveguides each disposed externally of one of said end cavities and adjacent one of said coupling holes; and

(1') loss means disposed in each of said waveguides for attenuating circuit wave energy.

9. A traveling-wave tube comprising in combination:

(a) collector means;

(b) electron gun means for emitting a stream of electrons;

(c) a solenoid for producing an axial magnetic field constraining said stream of electrons to flow along a predetermined path toward said collector means;

(d) a slow-wave structure divided into a plurality of amplifying sections and disposed between said electron gun means and said collector means for pro pagating circuit wave energy in such manner that it interacts with said stream of electrons;

(e) said slow-wave structure being disposed within and axially aligned with said solenoid and including means for precluding the passage of circuit wave energy between each pair of adjacent amplifying sections;

, (f) first and second waveguides, each disposed between said solenoid and said slow-wave structure and coupled to one of said adjacent amplifying sections of said slow-wave structure in the vicinity of said precluding means;

(g) the lengths of said waveguides being essentially parallel to the'axis of said slow-wave structure, and

(h) an attenuating element disposed in each of said waveguides for dissipating circuit wave energy.

10. A traveling-wave tube comprising in combination:

(a) collector means;

([2) electron gun means for emitting a stream of electrons;

(c) a solenoid for producing an axial magnetic field constraining said stream of electrons to flow along a predetermined path toward said collector means;

(d) slow-wave structure means for propagating circuit Wave energy disposed within said solenoid and between said electron gun means and said collector means;

(2) said slow-wave structure means comprising a plurality or" axially aligned apertured spacer elements and a plurality of vane members interposed between and projecting internally of the apertures in said spacer elements, said spacer elements and vane members defining a plurality of groups of intercoupled interaction cavities arranged sequentially along and in electromagnetic interacting relationship with said stream of electrons;

(f) means disposed between adjacent end cavities in adjacent ones of said groups for precluding the passage of circuit wave energy between said adjacent end cavities while permitting the passage of said stream of electrons therebetween;

(g) the respective spacer elements defining said end cavities each having a coupling hole through its lat eral surfaces;

(/1) a plurality of Waveguides, each disposed externally of said slow-wave structure in the vicinity of one of said end cavities and adjacent one of said coupling holes; and

(i) loss means disposed in each of said waveguides for attenuating circuit wave energy.

11. A traveling-wave tube of the type which is severed into a plurality of amplifying sections, each isolated from one another with respect to circuit wave energy comprising in combination:

(a) means for launching a stream of electrons along a predetermined path of fixed length;

(b) a wave propagating structure disposed along and about said path for propagating circuit wave energy in such manner that it interacts with said stream of electrons;

(0) means disposed between each pair of adjacent amplifying sections for precluding the passage of circuit wave energy between said adjacent amplifying sections while permitting the passage of said stream of electrons therebctwcen;

(d) terminated waveguiding means disposed externally of said wave propagating structure and coupled to said wave propagating structure adjacent said precluding means for propagating said circuit wave energy; and

(e) loss means disposed in said waveguiding means for attenuating the circuit wave energy propagated there- 12. A traveling-wave tube of the type which is severed into a plurality of amplifying sections, each isolated from one another with respect to circuit wave energy comprising in combination:

(a) means for launching a stream of electrons along a predetermined path of fixed length;

(1)) a wave propagating structure disposed along and about said path for propagating circuit wave energy in such manner that it interacts with said stream of electrons;

(0) means disposed between each pair of adjacent amplifying sections for precluding the passage of circuit wave energy between said adjacent amplifying sections while permitting the passage of said stream of electrons therebetween;

(d) terminated Waveguiding means disposed externally of said wave propagating structure and coupled to said wave propagating structure adjacent said precluding means for propagating said circuit wave energy; and

(e) non-magnetic reciprocal loss means disposed in said waveguiding means for attenuating the circuit wave energy propagated therein.

Zublin et al. June 7, 1960 Bates et al May 23, 1961 

1. A TRAVELING-WAVE TUBE OF THE TYPE WHICH IS SEVERED INTO A PLURALITY OF AMPLIFYING SECTIONS COMPRISING IN COMBINATION: (A) MEANS FOR LAUNCHING AN ELECTRON STREAM ALONG A PREDETERMINED PATH OF FIXED LENGTH; (B) SLOW-WAVE STRUCTURE MEANS IN EACH OF SAID AMPLIFYING SECTIONS AND DISPOSED ALONG SAID PATH FOR PROPAGATING CIRCUIT WAVE ENERGY AND PROVIDING ENERGY EXCHANGE BETWEEN SAID STREAM OF ELECTRONS AND SAID CIRCUIT WAVE ENERGY; (C) MEANS DISPOSED BETWEEN AT LEAST ONE PAIR OF ADJACENT AMPLIFYING SECTIONS FOR PRECLUDING THE PASSAGE OF CIRCUIT WAVE ENERGY BETWEEN SAID ADJACENT AMPLIFYING SECTIONS WHILE PERMITTING THE PASSAGE OF SAID ELECTRON STREAM THEREBETWEEN AND (D) MEANS DISPOSED EXTERNALLY OF SAID SLOW-WAVE STRUCTURE MEANS ADJACENT AT LEAST ONE END OF AT LEAST ONE OF SAID ADJACENT AMPLIFYING SECTIONS FOR ABSORBING CIRCUIT WAVE ENERGY. 